Known commercial thermoset resins from dendritic polymers such as acrylate and urethane thermosets have excellent processing and reactivity characteristics when compared to their linear polymer analogs due to their globular structure and high density of reactive functionalities. However, such thermoset materials may not be suitable for a wide range of electrical and electronic applications due to low thermal stability and moderate electrical properties. On the other hand, epoxy functionalized dendrimers have received little commercial success due to rheological issues associated with their extreme viscosities.
Dendritic polymers are a relatively new class of macromolecules with a hyperbranched structure formed from the incorporation of repetitive branching sequences by a multiplicative growth process beginning with a small molecule. As such, dendrimers typically consist of a core, from which branches extend in three-dimensions, forming a globular structure with a large number of end groups at the peripheral surface. Consequently, dendrimers differ significantly from conventional linear polymers in their physical properties. Their compact globular structure coupled with the absence of restrictive interchain entanglements results in low viscosities that are substantially lower than their linear polymer analogues of similar molecular weights as disclosed in “Properties and Applications of Dendritic Polymers”, B. Pettersson, Pyramid Communication AB, Sweden, 2001, and by R. Mezzenga, L. Boogh, and J. E. Manson, Composite Science and Technology, 61, 787, 2001, the disclosure of each expressly incorporated by reference herein. Furthermore, the variability in the chemical compositions of the core molecule, the chain extender, and the high density terminal groups allow for solubilities in a large variety of solvents.
To date, only a few dendritic polymers have been successfully commercialized. Among the commercial hyperbranched polymers are those that are based on polyalcohol and an aliphatic tertiary polyester backbone such as the structure shown in FIG. 1. They are sold under the trade name Boltorn™ by the Perstrop Specialty Chemicals (Boltorn is a trademark of Perstrop Specialty Chemicals). Most of the commercial applications of this family of dendritic polymers rely on the exceptionally high concentration of reactive hydroxyl groups that provide for a rapid curing in thermosetting applications. The most prominent applications are in the coating and in the polyurethane industries as discussed by D. James in the article “Parquet Coating II,” at the European Coating Conference, 14 Nov. 2002, the disclosure of which is expressly incorporated by reference herein. Currently, different Boltorn™ product grades are used by the radiation curable coating, the powder coating, the decorative coating, and the polyurethane industries in both automotive and non-automotive applications as discussed by D. James in PRA Radcure Coatings and Inks, 24 Jun. 2002, the disclosure of which is expressly incorporated by reference herein.
Although the application of dendritic polymers in epoxy resin compositions has been reported by L. Boogh, B. Pettersson, and J. E. Manson in Polymer, 40, 2249, 1999, the disclosure of which is expressly incorporated by reference herein, their utility in these instances is limited to their phase separation-induced toughening effect in the Bisphenol-A family type of epoxy resins that are cured by non-cationic initiation. Functionalization of the dendritic polymer with epoxy groups has also been reported and some commercial grades are available.